This invention relates to a swivel useful in transferring fluids and in particular to a multiple line swivel capable of transferring fluids between a plurality of fixed lines and a plurality of rotating lines. The invention is particularly useful in transferring fluids between ships and the ocean floor.
The offshore production of oil at substantial distances from land or in remote areas often makes it impractical to install a pipeline on the sea floor so that the oil produced from the offshore wells can be pumped directly to shore for storage and/or further transportation or processing. Oil produced under such circumstances is more conveniently delivered directly or by short feeder pipelines to a moored dedicated vessel, such as an oil tanker where it can be processed or stored until transshipment. Mooring a vessel offshore for extended periods presents many problems, including anticipated storm conditions at the mooring location. It is desirable for mooring systems to permit the vessel to weathervane or rotate so that the vessel will always face into prevailing seas, current and wind. A suitable mooring system for an offshore vessel which permits it to weathervane employs a pivoting assembly built into or attached to the vessel to allow for collection of oil or gas while the vessel is moved about or weathervanes.
Normally, a group of fluid lines extend from the ocean floor to the vessel. These fluid lines permit the transfer of a variety of fluids between the vessel and the ocean floor. For example, certain fluid lines may be used to convey the oil and/or gas into the vessel while other fluid lines may be used to inject liquids or gases back into the reservoir while still others may be used for hydraulic or other control functions. Although these fluid lines are somewhat flexible and thus permit some movement of the vessel, they are fixed to the ocean floor and will not rotate to any significant degree. Therefore, in order to convey the fluids between these flexible but fixed fluid lines and the rotating vessel, it is necessary to have a fluid swivel. Since some of these fluid lines may be rather large, since some of the fluids may be at high pressures and also at different pressures and temperatures from the fluids in other lines, a number of complications are introduced into providing a fluid swivel which will be both leakproof and functional. To date, the highest design pressure for a swivel is about 2,600 psi with an actual operating pressure of less than 1,000 psi.